Potentiation of antitumor effect of NKT cell ligand, alpha-galactosylceramide by combination with IL-12 on lung metastasis of malignant melanoma cells1

The combined therapeutic effect of natural killer T (NKT) cell ligand alpha -galactosylceramide (alpha -GalCer) and IL-12 against highly metastatic B1 6-BL6-HM melanoma cells was investigated. In comparison with a single admin istration of alpha -GalCer or IL-12, the combined treatment of tumor-bearin g mice with alpha -GalCer plus IL-12 caused a super-induction of serum IFN- gamma levels, though alpha -GalCer-induced IL-4 production was rather inhib ited. In parallel with the augmented IFN-gamma production, the natural kill ing activity against YAC-1 cells and syngeneic B16- BL6-HM melanoma was gre atly augmented by the combined therapy. The major effector cells responsibl e for natural killing activity induced by alpha -GalCer plus IL- 12 were en riched in both NK1.1(+)TCR alpha beta (+) NKT cells and NK1.1(+)TCR alpha b eta (-) NK cells. The preventing effect of alpha -GalCer or IL-12 alone aga inst lung metastasis of B16-BL6-HM was also enhanced by the combination the rapy. The antitumor activity of alpha -GalCer was totally abolished in NKT- deficient mice. However, IL- 12-induced antitumor activity was not eliminat ed in NKT-deficient mice though it was inhibited by anti-asialo GM1 Ab trea tment. These findings suggested that alpha -GalCer synergistically act with IL-12 to activate both NKT cells and NK cells, which may play a critical r ole in the strong prevention of distant tumor metastasis at early stages of tumor-bearing. These data will provide a novel tool for the prevention of tumor metastasis using NKT-specific ligands alpha -GalCer and IL-12.